The present invention relates generally to a thin film solar module and, more particularly, to a method and structure for interconnecting cells by a plurality of discrete conductive regions extending between each pair of cells to be interconnected.
Thin film solar cells generate current at voltages far below those required in most consumer applications. Thus, it is desirable to produce a large number of such cells in a single monolithic module and connect them in series so that the overall output voltage is the sum of the cell voltages. A number of prior techniques for interconnecting monolithic solar cells have made use of continous stripes of conductive material disposed along edges of the cells, as described in Kim U.S. Pat. No. 4,428,110, Biter U.S. Pat. No. 4,042,418 and Swartz British Pat. No. 2,095,908.
Another form of interconnection is disclosed in the above-identified parent application of Morel et al, which describes a primary embodiment having conductive stripes or "stitch bars" on transparent front contact pads. Unlike the stripes of the Kim, Biter and Swartz patents, the stitch bars of the Morel patent are not necessarily continuous.
The Morel technique also makes use of the localized application of heat to the area of the stitch bars to increase conductivity. If a laser of sufficiently high energy is used to apply heat, the back contact and the semiconductive layer beneath it are cut along a continuous line, leaving a conductive residue which connects the cells together. However, such a cut isolates one-half of the conductive residue from the bulk of the corresponding back contact pad, taking that portion of the residue out of the series circuit of the module.
A continous cut is also undesirable for process-related reasons because the laser used to produce it must emit pulses rapidly as the workpiece moves. This requires a rather sophisticated laser and may limit the processing speed. Finally, continuous cutting operations produce a significant amount of debris which can be a problem in cell manufacture.
Therefore, it is desirable to provide an improved method of interconnecting monolithic solar cells which is rapid, effective, and produces a minimum of debris.